Seat cushions currently used in automotive, aircraft, and military vehicles are generally passive in nature. That is, they rely on the use of rate sensitive foams to cushion occupants and absorb energy transmitted from routine vehicle use, as well as from high energy events such as impacts and the catapult phase of an ejection in the case of aircraft. While these foams may reduce the probability of injury by slightly lowering the spinal loads to which an occupant is exposed, they have several limitations. Conventional passive foams are very sensitive to environmental conditions such as temperature, humidity, and age. Each of these conditions reduces the effectiveness of the foams. As such, their performance is generally difficult to accurately quantify or predict. In addition, their passive nature prevents them from adjusting to the contours of each individual or adjusting to a particular impact event. Conventional passive foams also do little to isolate and minimize vibrations transmitted to occupants during routine use of various vehicles such as automobiles and other ground vehicles, airplanes, and rotorcraft.
With the increased tempo of military operations, including combat missions that may extend to 40 hours or more, such limitations can adversely affect air crew comfort and effectiveness. Moreover, current ejection seats create discomfort, soreness, and numbness and increase overall operator fatigue, particularly during extended missions. Another limitation of passive cushions is that they can only absorb a certain amount of energy in a particular way and therefore cannot be designed to provide optimal support and energy absorption for different conditions such as different-sized occupants and different impact levels. Typical designs of passive cushions are directed to mid-sized males. If a heavier person uses the system, the cushion may be pre-compressed beyond the point at which it has been designed to absorb any additional impact energy. Conversely, if a smaller person uses the system, he or she may not sufficiently load the system during impact to absorb the energy. These are inherent limitations found in current designs that use passive cushions and foams.